1. Field of the Invention
The present invention relates generally to the field of viscous damping apparatus. More particularly, the present invention relates to viscous damping apparatus incorporated with load cells of weighing devices.
2. Description of the Prior Art
The following most pertinent prior art patents have been uncovered and deemed to be relevant to the present invention:
1. U.S. Pat. No. 4,479,561 issued to Feinland et al. on Oct. 30, 1984 for "Weighing Cell" (hereafter referred to as the "Feinland patent").
2. U.S. Pat. No. 4,201,081 issued to Bonomo on May 6, 1980 for "Pressure Responsive Sensing Device" (hereafter referred to as the "Bonomo patent").
3. U.S. Pat. No. 4,009,604 issued to Taber et al. on Mar. 1, 1977 for "Pressure Converter For Calibrating Gauges" (hereafter referred to as the "Taber patent").
4. U.S. Pat. No. 3,991,841 issued to Crawley on Nov. 16, 1976 for "Weighing Device" (hereafter referred to as the "Crawley patent").
5. U.S. Pat. No. 3,982,738 issued to Meier et al. on Sep. 28, 1976 for "Dash-Pot Arrangement For Balance" (hereafter referred to as the "Meier patent").
6. U.S. Pat. No. 3,876,017 issued to Ziefle on Apr. 8, 1975 for "Scale Construction" (hereafter referred to as the "Ziefle patent").
7. U.S. Pat. No. 3,789,873 issued to Westwood on Feb. 5, 1974 for "Pneumatic Pressure Transmitting Device" (hereafter referred to as the "Westwood patent").
8. U.S. Pat. No. 3,842,924 issued to Schmitter et al. on Oct. 22, 1974 for "Damping Arrangement For A Balance" (hereafter referred to as the "Schmitter patent").
9. U.S. Pat. No. 1,837,817 issued to Hallead on Dec. 22, 1931 for "Damping Mechanism For Scales" (hereafter referred to as the "Hallead patent").
The Hallead patent (1931) discloses a damping mechanism for a scale. The Hallead patent damping apparatus comprises an inner cylinder 15 having an inner chamber for containing viscous fluid, and an outer cylinder 1 providing an annular outer chamber for by-passing the viscous fluid. The inner cylinder 15 has several upper sidewall apertures 21 and a lower bottom opening for interchanging the viscous fluid with the annular outer chamber. A piston 14 is assembled inside the inner chamber and connected to the lever 10 of the scale by a piston rod 12. When the piston 14 moves up and down inside the inner chamber, its movement is dampened by the vicious fluid, which in turn is forced to pass through the by-pass annular outer chamber. The Hallead patent provides one of the basic models of the piston-cylinder type viscous damping apparatus for scales and balances. For the piston-cylinder type damping apparatus to function properly, it is essential to have the piston well conform with the cylinder, i.e., the diameter of the piston plate should be very close to the diameter of the inner chamber of the cylinder.
The Schmitter patent (1974) discloses a damping arrangement for a balance. The Schmitter patent damping apparatus comprises two identical dashpots 9a and 9b. The dashpot 9a includes a glass tube 19 and a plunger 12 carrying two annular piston rings 14, which are free to move radially into direct contact with the inner surface of the glass tube 19. The arrangement of the piston rings 14 regulates the air passage between the inside and outside of the glass tube for providing pneumatic damping to the plunger 12, which is further connected with the balance arm.
The Westwood patent (1974) discloses a pneumatic pressure transmitting device utilizing a damping apparatus for damping the movement of the cover 4 of its pneumatic pressure chamber 1. The Westwood patent damping apparatus comprises an annular damping plate submerged in oil 16 contained at the bottom of a cup 14.
The Ziefle patent (1975) discloses a scale construction utilizing a piston-cylinder type damping apparatus. The Ziefle patent piston-cylinder type damping apparatus comprises a cylinder 1 containing oil 5 and a piston 7 connected with a balance lever 12 through a piston rod 8. The diameter of the piston 7 is slightly smaller than the inner diameter of the cylinder 1 for providing proper damping.
The Meier patent (1976) discloses a dashpot arrangement for a balance. The Meier patent damping apparatus comprises a piston 24 which is immersed in a body 10 of oil enclosed in a cylindrical vessel 12. The diameter of the piston 24 is, again, slightly smaller than the inner diameter of the cylindrical vessel 12 for providing proper damping.
The Crawley patent (1976) discloses a weighing device having a damping apparatus. The Crawley patent damping apparatus comprises a container 9 containing viscous fluid, and a rod 4 extending into the container 9. A washer 10 is fitted at the bottom of the rod 4 and submerged in the viscous fluid for damping the movement of the rod 4. The size of the washer 10 does not match the size of the inner chamber of the container 9.
The Taber patent (1977) discloses a pressure converter which can be used between a load cell and a gauge. The Taber patent apparatus is not a damping apparatus for the load cell, but rather a calibrating apparatus for the gauge.
The Bonomo patent (1980) discloses a pressure responsive sensing device. The Bonomo patent apparatus is merely a pressure transducer.
The Feinland patent (1984) discloses a weighing cell having a platform 3, a self-contained base 4 and a load cell 1 operatively connected therebetween. Shims 11 and 14 are provided on the upper and lower surfaces of the load cell 1 to maintain pre-determined partial gaps between the load cell 1, the platform 3 and the base 4.
Most of the prior art patents utilize piston-cylinder type viscous damping apparatus for damping the weight head or load cells of scales. The general features of such prior art damping apparatus are illustrated in FIG. 1 at 10. The damping apparatus 10 is used for damping the vibration of an external object such as a load cell 11. It comprises a cylindrical shaped container 12 containing a body of viscous fluid 14. A damping plate 16 is positioned in the middle of the container and connected to the load cell 11 through a piston rod 18. To provide adequate damping effect, the damping plate 16 of this prior art piston-cylinder type damping apparatus 10 has to match the inner circumferential size of the vicious fluid container 12, which often results in inaccurate reading on the load cell 11 because of the friction due to the physical contact between the damping plate 16 and the inner sidewall of the viscous fluid container 12. It is desirable to have a damping device, wherein the contact between the damping plate and the inner sidewall of the viscous fluid container is completely avoided; but which still provides adequate damping effect.